A recently developed type of secondary battery or rechargeable electrical conversion device comprises: (1) an anodic reaction zone containing a molten alkali metal anode-reactant, e.g., sodium, in electrical contact with an external circuit; (2) a cathodic reaction zone containing a cathodic reactant comprising a liquid electrolyte, e.g., sulfur or a mixture of sulfur and molten polysulfide, which is electrochemically reversibly reactive with said anodic reactant; (3) a solid electrolyte comprising a cation-permeable barrier to mass liquid transfer interposed between and in contact with said anodic and cathodic reaction zones; and (4) a current collector which is in electrical contact with both said cation-permeable barrier and said external circuit. As used herein the term "reactant" is intended to mean both reactants and reaction products.
One of the primary problems which must be overcome before the alkali metal/sulfur cells or batteries of the above type become commercially feasible involves materials. In particular, that problem involves the selection of current collector and/or container or liner materials which will be stable in corrosive polysulfide salts generated during discharge of the cell or battery. While metals are likely candidates for use as current collectors and/or containers or liners since they are conductive and nonporous, they tend to corrode in the presence of polysulfide salts. Graphite, on the other hand, is fairly noncorrodable in polysulfide melts and is conductive, but is porous to the melt and gases generated during operation of the cell and tends to oxidize in the presence of air.
It is an object of this invention to provide an improved battery or cell of the above type wherein the current collector and/or container or liner is not only conductive and non-corrosive as in the case of graphite, but is also nonporous as in the case of metals.